Drain the canned peaches and cut into small pieces. Pour the amaretto over the amarettini in a bowl and let them soak for 10 minutes. In a separate bowl, whip the cream until stiff peaks form, about 3-5 minutes.
Mix the crème fraîche with the quark, powdered sugar, and vanilla sugar until smooth. Carefully fold in the soaked amarettini. Gently fold in the whipped cream.
Divide part of the cream mixture into serving glasses. Layer peaches on top of the cream in each glass, then cover with another layer of cream mixture. Refrigerate for 2 hours.
Garnish each serving with crushed amarettini crumbs and chopped pistachios, or with peach pieces and pistachios.